1. Field
This disclosure relates to a croconaine compound and a method for making the same.
2. Background
Photodynamic therapy (PDT) is a form of light therapy, sometimes called phototherapy, using nontoxic light-sensitive compounds which become toxic when exposed to particular wavelengths of light, thereby disrupting the function of malignant or other diseased cells. PDT requires three key components: a photosensitive compound, a light source, and tissue molecular oxygen. When the compound is irradiated, it excites neighboring tissue oxygen to create reactive oxygen species which, in turn, react with surrounding tissue and disrupt various cell functions. A limitation of this method is that it is often not useful in hypoxic tissue. Additionally, many organic compounds are subject to photobleaching as well as degradation from interaction with the produced reactive oxygen species.
Photothermal therapy (PT) offers a related, but simpler and more widely applicable, method of phototherapy utilizing photothermal heating. Photothermal heating occurs when light energy is absorbed by the compound and released by non-radiative means. There is significant technical advantage to using non-ionizing, near-infrared light, especially light with wavelengths that are close to 800 nm, as it is less harmful to healthy living tissue and is capable of deep tissue penetration, which facilitates many procedures based on photothermal heating. Gold nanoparticles or nanorods are the best-known absorbing systems for PTT; however their large size, slow rates of diffusion, propensity to melt, potential for toxic buildup, and relative synthetic inflexibility limit their application. Current near-infrared absorbing organic compounds, although perhaps otherwise suitable, suffer from photobleaching, inefficient conversion of light into heat, and a propensity to produce reactive oxygen species. Although the latter feature is useful for PDT it is not useful in many photothermal applications such as drug release. For the aforementioned reasons, there is a need for biologically compatible, chemically stable, and synthetically flexible compounds which upon laser irradiation in the wavelength 750-850 nm provide efficient photothermal heating with very low production of reactive oxygen species and very low photobleaching.